Production of 3-methyl-1-butene



Nov. 8, 1966 .w. R. EDWARDS ETAL 3,284,535

PRODUCTION OF 5-METHYL-l-BUTENE Filed May 10, 1953 ISOPENTANE a LIGHTERC4AND LIGHTER FRACTIONATOR L'/-FRACTI0NATOR I99 3-METHYL-l-BUTENEISOMERIZATION I22 ZONE c TO 430 F. CATALYTIC NAPHTHA STREAM 4 no I9 aHEATER I|2 I04 BOTTOMS BLEED INVENTQR.

WILLIAM R. EDWARDS, ROBERT D. WESSELHOFT, BY WILLARD N. MITCHELL,

ATTORNEY United States Patent 3,284,535 PRODUCTIQN OF 3-METHYL-1-BUTENEWilliam R. Edwards, Robert D. Wesselhoft, and Willard N. Mitchell,Baytown, Tern, assignors, by mesne assignments, to Esso Research andEngineering Company,

Elizabeth, N..l., a corporation of Delaware Filed May 10, 1963, Ser. No.279,357 4 Claims. (Cl. 260-6832) The present invention relates to theproduction of 3-methyl-l-butene from catalytic naphtha. Moreparticularly, it relates to the production of 3-methyl1-butene fromisomers thereof which are present in catalytic naphtha by a processwhich economically yields 3-methyl-1- butene in high purity withoutexpensive aftertreatment.

-High purity B-methyl-l-butene currently may be obtained byfractionation and purification of catalytic naphtha to recover the3-methyl-1-butene which is present therein. However, this purificationprocess involves a number of steps, such as contacting the3-methyl-l-butene with molecular sieves, and is expensive.

The amount of 3-methyl-l-butene recoverable from catalytic naphtha bycurrently known processes is limited by the amount of catalytic crackingactivity. Based on normal catalytic cracking operations, only about 12barrels of 3-methyl-1-butene are produced for every 10,000 barrels offeed charged to the catalytic cracker. Further, the recovery ofZ-methyl-l-butene involves the use of very large fractionation andrecovery facilities, which adds to the difiiculty and expense inrecovering a high purity 3-metl1y1-1-butene product.

The present invention provides a process whereby large amounts of3-methyl-1-butene may be produced from catalytic naphtha, whileminimizing the fraction ation facilities required and providing aneconomical method of producing 3-methyl-l-butene of the highest purity.

The present invention may be briefly described as fractionating a C to430 F. catalytic naphtha in order to obtain a heart cut which containscompounds boiling from pentene-l through Z-methyl'butene-Z. Almost allof the included compounds may be isomerized to 3-rnethyll-butene and aretherefore termed precursors of 3-methy1-1-butene. This heart cut isisomerized over an acid catalyst in order to obtain roughly thermalequilibrium amounts of Z-methyl-l-butene, which is separated andrecovered from the isomerized product. The precursors of3-methyl-1-butene in the product stream may be recycled virtually toextinction, only a small amount of purge being required. Thus, from 50%to 75% yield of 3-methyl-1-butene (based on the catalytic naphtha heartcut) may be recovered, as compared to only about 3% in the C portion ofthe catalytic naphtha. Allowing for the relative volumes of the twostreams, this indicates a recovery of to times as much 3-methyl-1-butene by the present invention as could be recovered by knownprocesses.

The catalytic naphtha feedstock of the present invention is obtained bycatalytically cracking hydrocarbons over a catalytic cracking catalyst,such as silica-alumina, at a temperature of about 900 F. to 975 R,either in a fixed bed or in a transfer line reactor. The reactionproduct is fractionated and a debutanized, olefin-containing streamboiling from C through 430 F. is recovered. This catalytic naphthastream provides the feed material .for the present invention.

An exemplary catalytic naphtha boiling from C through 430 F. may containthe following lower boiling compounds:

TABLE I Compound: Boiling point, F. 3-methyl-I-butene 68 1,4-pentadiene79 Isopentane 82 Pentene-l 86 Z-methyl-l-butene 88 Pentene-2 97n-pentane 97 Z-methyl-Z-butene 101 Note that both isopentane and1,4-pentadiene have higher boiling points than 3-methyl-1-butene, sothat it is necessary to remove the 3-methyl-1-butene along with theisopentane and 1,4-pentadiene. It has been found that the3-methyl-l-butene produced by the present invention is superior to thatremoved in the first step, since no 1,4- pentadiene is present in theisomerized product.

The first fractionation may be accomplished in one step or as part ofthe usual depentanization of catalytic naphtha, wherein the butanes andthen the pentane hydrocarbons are removed from the total catalyticnaphtha stream. By either expedient, a catalytic naphtha feed.- stock tothe first fractionator is obtained, from whence a heart cut is obtainedwhich consists essentially of pentene-l, Z-methyl-l-butene, pentene-Z,n-pentane, and Z-methyI-Z-butene. Each of these materials is a precursorof 3-methy1-1-butene. Some isopentane may be tolerated in the heart cut,as is hereinafter more clearly set forth.

In the first fractionation step, isopentane is selectively removedoverhead, as little as possible of the isopentane being carried overinto the heart cut. In removing the isopentane, 3-methyl-l-butene whichoccurs in the catalytic naphtha will also pass overhead and be lost fromthe charge stock. The isopentane must be substantially removed eventhough this results in the loss of the 3-methyl-l-butene, since theisopentane may comprise 30 mol percent of the C fraction of thecatalytic naphtha. This large amount of isopentane would make itimpossible to use a desirably high recycle ratio in the isomerizationzone, since it would tend to build up and. (since isopentane is not aprecursor of 3-methyl-1-butene) its diluent effect eventually wouldcause the reaction to become inoperable. Also, by removing theisopentane as an overhead stream, 1,4-pentadiene is removed from thefeedstock. In addition, removal of the isopentane from the isomerizationfeed greatly simplifies the distillation required to recover3-methyl-l-butene from the isomerization product. The 3-niethyl-l-buteneproduced. by isomerization is thus recovered as a final product,uncontaminated with this diolefin. Where the 3-1nethyl-1-butene isintended for certain purposes, such as polymerization, the completeexclusion of 1,4-pentadiene is necessary.

Since commercial scale fractionation facilities usually do not make aprecise component separation, at certain amount of the isopentane may becarried over into the heart cut. Up to about 5 mol percent of isopentanemay be tolerated in the heart cut, if the purge stream from theisomerization recycle line is adjusted to account for the isopentanewhich is carried into the isomerization zone with the feedstock. Ineffect, the more isopentane in the heart cut, the higher the purge rate,the lower the recycle ratio to the isomerization zone, and the moreexpensive the product fractionation. 1,4-pentadiene, however, isrigorously excluded from the feedstock since this product would not beseparable from the 3-methylbutene-1 product, at least to the extentrequired in producing a polymerization grade S-methyl-l-butene.

In the isomerization zone, the heart cut is contacted with a solidacidic catalyst such as a cracking catalyst. Cracking catalysts whichare suitable for use would include the 3A silica-alumina catalyst,silica gel, and alumina.

The isomerization is accomplished at a temperature within the range ofabout 600 F. to about 1200 F., from 800 F. to 1000 F. having been foundto be preferable. The pressure in general is immaterial and may becarried out either at atmospheric, subatmospheric, or superatmosphericpressures. It is preferred to operate in the range of atmosphericpressure, however. The space velocity may range from about 5 to about 25v./v./hr., a preferred range being from 8 to v./v./hr. Residence timemay range from 0.2 second to 1.2 seconds.

The isomerized product from the isomerization zone will contain3-methyl-1-butene in amounts approaching the thermal equilibrium valuesthereof.

The isomerized product is passed from the isomerization zone throughrequisite heat exchangers and coolers and is charged into a finalfractionator wherein the isomerized product is separated into a3-methyl-1-butene product stream, a C and lighter product stream (whichrepresents the light products of cracking in the isomerization zone),and a bottoms stream which is recycled to the isomerization zone inorder to obtain a conversion of 50% to 75% to 3-methyl-1-butene, basedon the hydrocarbons charged. A portion of this recycle stream may bebled from the system in order to prevent the build-up of diluents in theisomerization zone.

All of this may be more clearly understood by reference to the drawingwherein a preferred mode of practicing the present invention is setforth.

Referring now to the drawing, a C to 430 F. catalytic naphtha stream,which comprises 34methyl-1-butene, isopentane, pentene-l, 2-rnethyl-1butene, pentene-2, Z-methyl-2-butene, and n-pentane, is charged by wayof line 99 into a fractionator 100. Isopentane and lighter materials aretaken off overhead by way of line 102, while materials heavier than2-methyl-2butene are taken off as a bottoms stream through line 104. The1,4-pentadiene-free heart cut consisting essentially of l-pentene,2-methyl-1- butene, Z-pentene, n-pentane, and 2-methyl-2-butene isremoved as a side-stream from the tower by way of line 106 and is passedthrough a heater 108 where the temperature is raised to about 925 F.

The heart out feedstock to the isomerization zone is then passed by wayof line 110 and contacted with a recycle stream introduced by way ofline 112, to be introduced into the isomerization zone 114. Within theisomerization zone, the admixture of heart cut and recycle stock iscontacted with an acid catalyst such as a 3A cracking catalyst at about925 F. for about 0.4 second. The space velocity may be about 13v./v./hr.

From the isomerization zone 114, an isomerized prodnot is withdrawn byway of line 116 and introduced into the second fractionator 118.

From the second fractionator 118, the cracking fragments from theisomerization zone are removed as C and lighter materials through line120, while 3-methyl-1- butene is removed as a substantially pure productstream by Way of line 122. The bottoms stream from the fractionator 118comprises 3-methyl-1-butene precursors plus the isopentane, if any,which have been carried through the system. This bottoms stream isdischarged by way of line 124, and a bleed stream removed by way of line126. The recycle stream is carried from line 124 back into contact withthe catalyst in the isomerization zone by line 112.

Thus, it is apparent that the present invention provides a simple andeconomical method of producing high purity 3-methyl-1-butene with anultimate recovery of 50% to 75 based on the heart cut feedstock to theisomerization zone.

More than ten times the amount of 3-methyl-1-butene present in catalyticnaphtha may be produced by converting 3-methyl-1-butene precursors into3-methyl-1-butene, recycling the precursors to the isomerization zone toobtin 50% to 75% conversion thereof.

It is to be noted that by the practice of the present invention, whereinthe large amounts of isopentane present in the catalytic naphthafeedstock are discarded before isomerization, the final fractionationfacilities are only about one-third the size of that required if3-methyll-butene is to be recovered as a naturally occurring productstream. Further, the expensive aftertreatment of the 3- methyl-l-butene(e.g., contacting with molecular sieves) is avoided by the practice ofthe present invention, and a polymerization grade product is obtained asthe final product.

As exemplary of the present invention, a number of runs were made.

Example 1 A C to 430 F. catalytic naphtha was debutanized and thendepentanized. The second step yielded a C fraction which was thencharged to a first-stage fractionator. A heart out in accordance withthe present invention was obtained, and this heart out was isomerizedover 3A silicaalumina catalyst at a temperature of 900 F. and a pressureof 0 p.s.i.g. The residence time was about 0.4 second, the spacevelocity being about 13.0 v./v./hr. The isomerized product wasfractionated in order to recover a product stream containing3-methyl-1-butene.

The results are summarized in the table below.

TABLE II Isomcrization (15's Cat. Naphtha, Feed, Mol Food, Product,

Percent M01 M01 Percent Percent 0. 2 0 O 5. 0 2. 6 5. 5 l5. 0 7. 5 17. 815. 0 21. 1 1G. 3 7. 5 13. 2 8. 8 23. O 46. 7 36. 0 n-Pentane 4. 0 4. 75. 1

Example 2 A run similar to Example 1 was made at 975 F. rather than 900F. The heart cut was contacted with 3A silicaalumina catalyst at 975 F.,0 p.s.i., space velocity of 13.8 v./v./hr., and a residence time of 0.4second. The product from the isomerization zone had the followingcomposition:

TABLE III Mol, percent (34 8 3-methyl-1-butene 3.0 Isopentane 3.8n-Pentane 5.2 Pentene-l 6.3 Z-methyl-l-butene 17.3 Trans-Zpentene 18.3Cis-2-pentene 10.6 2-methyl-2 butene 34.9

Raising the temperature from 900 F. to 975 F. had no appreciable effecton the product distribution.

Thus, it is seen that the production of 3-methyl-1-butene from catalyticnaphtha may be increased by a fact-or of 10, while economicallyobtaining a product of high purity.

Having disclosed the essence of our invention and having set forth thepreferred modes of practicing it, what is to be covered by LettersPatent should be limited not by the specific examples herein given, butonly by the scope of the appended claims.

We claim:

1. A method of optimizing the production of high purity3-methyl-l-butene from catalytic naphtha which comprises fractionatingsaid catalytic naphtha to exclude isopentane and lighter compounds andcompounds heavier than 2-methyl-2-butene,

whereby a heart out is obtained consisting essentially of pentene-l,2-methyl-l butene, pentene-Z, normal pentane, and 2-methyl-2 butene,each of which is a precursor of 3-methyl-1- butene,

contacting said heart cut in an isomerization zone with a silica-aluminacracking catayst at a temperature of 800 F. to 1000 F. and a spacevelocity of 5 to 25 v./v./hr. to obtain an isomerized product streamcontaining more 3-rnethyl-1- butene than Was contained in said heartcut,

fractionating said isomerized product stream to obtain a-3-methyl-1-butene stream and a recycle stream, recovering said3-methyl-l-butene,

and recycling said recycle stream to said isomerization zone.

2. A method of optimizing the production of high puritySnnethyl-l-butene from catalytic naphtha which comprises fractionatin-gsaid catalytic naphtha to obtain a heart out consisting essential-1y ofpentene-l, 2-rnethyl-1- butene, pentene-Z, napentane, and2-methyl-2-butene, each of which is a precursor of 3-methyl-1-butene,and containing less than 5% isopentane, and being free of1,4-pentadiene,

contacting said heart cut in an isomerization zone with a silica-aluminacracking catalyst at a temperature of 800 F. to 1000 F. and a spacevelocity of 5 to 25 v./v./hr. to obtain an isomerized product streamcontaining more 3-methyl-1-butene than was contained in said heart cut,

fractionating said isomerized product stream to obtain a 3-methyl-1butene stream and a recycle stream, recovering said 3-methyl-1-butene,

and recycling at least a portion of said recycle stream to saidisomerization zone.

3. A method of optimizing the production of high purity3-methy1-1-butene from catalytic naphtha which comprises tractionatingsaid catalytic naphtha to obtain a heart cut consisting essentially ofpentene-l, Z-methyl-bbutene, pentene-Z, n-pentane, andZ-methyI-Z-butene, each of which is a precursor of 3-methy1-1-butene,and isopentane being present in amounts less than 5.0%,

contacting said heart cut in an isomerization zone with an acidiccracking catalyst at a temperature of 800 F. to 1000 F. and a spacevelocity of 5 to 25 v./v./hr. to obtain an isomerized product streamcontaining more 3-methyl-l-butene than was contained in said heart cut,

fractionating said isomerized product stream to obtain a3-methyl-1-butene stream and a recycle stream, and recyling at least aportion of said recycle stream to said isomerization zone. 4. A methodof optimizing the production of high purity 3-methyl-1 butene fromcatalytic naphtha which comprises fractionating said catalytic naphthato obtain a heart cut consisting essentially of pentene-l,2-methyl-lbutene, pentene-Z, n-pentane, and 2-methyl-2-butene, each ofwhich is a precursor of 31methy l-1-butene,

contacting said heart out in an isomerization zone with an acidiccracking catalyst under isomerization conditions to obtain an isomerizedproduct stream containing more 3-methyl-l-butene than was contained insaid heart cut,

fractionating said isomerized product stream to obtain a 3-methyl-lbutene stream and a recycle stream, and recycling at least a portion ofsaid recycle stream to said isomerization zone.

References Cited by the Examiner UNITED STATES PATENTS 2,463,873 3/1949Heinrich 260-6832 2,900,425 8/1959 Bloch et a1. 260-683.75 3,173,9683/1965 Edwards et al 260-683.2

OTHER REFERENCES Ewell et al.: Isomerization Equilibrium Among theBranched Chain Pentenes, Journal of the American Chemical Society, vol.63, pp. 3460-3465, 1941.

Oblad et al.: Isomerization of 1- and Z-Pentenes, Industrial &Engineering Chemistry, vol. 39, No. 11, November 1947, pp. 14624466.

DELBERT E. GANTZ, Primary Examiner. R. SHUBERT, Assistant Examiner.

4. A METHOD OF OPTIMIZING THE PRODUCTION OF HIGH PURITY3-METHYL-1-BUTENE FROM CATALYSTIC NAPHTHA WHICH COMPRISES FRACTIONATINGSAID CATALYTIC NAPHTHA TO OBTAIN A HEART CUT CONSISTING ESSENTIALLY OFPENTENE-1, 2-METHYL-1BUTENE, PENTENE-2, N-PENTANE, AND2-METHYL-2-BUTENE, EACH OF WHICH IS A PRECURSOR OF 3-METHYL-1-BUTENE,CONTACTING SAID HEART CUT IN AN ISOMERIZATION ZONE WITH AN ACIDICCRACKING CATALYST UNDER ISOMERIZAITION CONDITIONS TO OBTAIN ANISOMERIZED PRODUCT STREAM CONTAINING MORE 3-METHYL-1-BUTENE THAN WASCONTAINED IN SAID HEAT CUT, FRACTIONATING SAID ISOMERIZED PRODUCT STREAMTO OBTAIN A 3-METHYL-1-BUTENE STREAM AND A RECYCLE STREAM, AND RECYCLINGAT LEAST A PORTION OF SAID RECYCLE STREAM TO SAID ISOMERIZATION ZONE.